Embodiments herein generally relate to printing devices and other machines that utilize media paths to feed and register media sheets and more particularly to a registration system that utilizes multiple diagonal elongated sensors to determine the skew and position of the media sheet.
Sheet transport and registration systems often require sheet position and/or sheet dimension measurements. For example, sheet registration systems measure sheet position for use by a sheet controller to position the sheet to a datum. Sheet position is commonly measured in three degrees of freedom, a.k.a. process (lead edge), lateral (side edge) and skew (angle). This requires multiple sensors. For second side imaging, sheet trailing edge sensing may also be used. This increases the number of sensors at a substantial expense.
The embodiments herein describe methods and devices in sheet registration systems which use two or more array sensors to measure sheet position in three degrees of freedom, process position, lateral position and skew. A sensor may measure two or more different edges of the sheet simultaneously. This reduces the overall number of sensors resulting in substantial cost saving.
Disclosed herein is an apparatus, such as a printing apparatus (e.g., an electrostatic or xerographic machine) that has a media path and alignment devices (moving devices, such as rollers, belts, air movement devices, etc). The alignment devices move a media sheet in a processing direction of the media path. At least two elongated sensors are positioned adjacent the alignment devices within the media path. The elongated sensors are positioned diagonally relative to the processing direction of the media path.
The media sheet is generally rectangular and includes a front side and a backside and two lateral sides, a leading edge, and a trailing edge. A marking device is positioned adjacent the alignment devices within the media path. The marking device prints markings on the media sheet.
The elongated sensors each comprise an array of light sensitive pixels. The elongated sensors are positioned, relative to the media path, such that the elongated sensors simultaneously detect one of the lateral sides, and either the leading edge or the trailing edge of the media sheet. The elongated sensors are positioned at a diagonal angle with respect to the media path and the processing direction. In other words, the elongated sensors are at an angle other than parallel to, and other than perpendicular to the sheet processing direction.
Thus, each of the elongated sensors simultaneously identifies a location of one of the lateral sides of the media sheet, and either the leading edge or the trailing edge of the media sheet. Thus, a combination of the elongated sensors simultaneously outputs at least two lateral measures of locations of the lateral sides of the media sheet (each sensor outputs one position of one lateral side of the media sheet and the two combined sensors output two lateral measures). Also, the combination of the elongated sensors simultaneously outputs at least one leading edge measure of a position of the leading edge of the media sheet and/or at least one trailing edge measure of a position of the trailing edge of the media sheet (each of the sensors detects either the leading edge or the trailing edge and the two combined sensors output one or both measures).
A registration controller is operatively connected to (directly or indirectly connected to) the media path and to the elongated sensors. The registration controller utilizes at least three simultaneous measures (comprising the two lateral measures; and the leading edge measure and/or the trailing edge measure) to determine the skew and position of the media sheet. Skew can be determined from the difference of the two lateral measurements. In addition, lateral position measurement (for lateral alignment) is measured by either sensor or a weighted average. Process position (for process alignment) is measured by sensors. The choice depends on whether lead edge or trail edge alignment is to be achieved. Skew can be determined from the difference of the two lead edge measurements. Process and lateral measurement can use either sensor or a weighted average. The registration controller calculates a registration correction factor based upon the skew and alters the actions of the alignment devices based on the correction factor to correct the skew. The registration controller also calculates a registration correction action based on the position (lateral and process direction) of the sheet and alters the action of the alignment devices to correct for the position.
Embodiments herein also comprise method embodiments. For example, one method embodiment moves the media sheet along the media path in the processing direction using moving devices within the media path. The method uses at least two elongated sensors within the media path positioned diagonally relative to the processing direction to simultaneously identify a location of at least one of the lateral sides of the media sheet and the leading edge and/or the trailing edge of the media sheet. Again, the combination of the elongated sensors simultaneously outputs at least two lateral measures of locations of the lateral sides of the media sheet and outputs at least one leading edge measure of a position of the leading edge of the media sheet and/or at least one trailing edge measure of a position of the trailing edge of the media sheet.
Utilizing the lateral measures and at least one of the leading edge measure(s) and/or the trailing edge measure(s), the registration controller determines the skew and position of the media sheet using a registration controller. Skew can be determined from the difference of the two lateral measurements. In addition, lateral position measurement (for lateral alignment) is measured by either sensor or a weighted average. Process position (for process alignment is measured by sensors. The choice depends on whether lead edge or trail edge alignment is to be achieved. Skew can be determined from the difference of the two lead edge measurements. Process and lateral measurement can use either sensor or a weighted average. The registration controller also calculates the registration correction factor based upon the skew, and alters actions of the moving devices based on the correction factor to correct the skew. These and other features are described in, or are apparent from, the following detailed description.